A content delivery network or CDN may comprise multiple servers which cooperate with each other to send digital content to user terminals. However, a user can only access the digital content if he meets certain criteria. Access to digital content can be controlled for example on the basis of a subscription which gives the user access to certain digital content, or on the basis of a payment made for each access to a digital content item.
To achieve this, the architecture of such a network is based partly on a service subnetwork, which handles verifying whether a user terminal has the right to access the digital content the user is requesting, and partly on a digital content distribution subnetwork, which handles sending the digital content to a user terminal that has requested it. In this type of content delivery network, it is important to establish security measures which control access to the delivered content.
In such an architecture, a user terminal first requests a digital content item from the service subnetwork. Then, once this service subnetwork has decided that the user terminal has the right to access the requested digital content, it responds to this request by redirecting the terminal to one or more elements of the digital content distribution subnetwork able to deliver the requested digital content to the user, or digital content servers.
In order to control and ensure the security of the distribution of this digital content to a user terminal, the service subnetwork can be set up to respond to the user terminal by indicating:                a URL (Uniform Resource Locator) address; and        a token.        
Then the user terminal uses this URL address and this token to request the content concerned from the digital content server or servers.
Under these conditions, the digital content server provides the requested digital content to the user terminal only if the token is considered to be valid. Such a mechanism provides secure access to the digital content.
However, even if the distribution subnetwork verifies the token before distributing the digital content, this mechanism is based on a security measure which is applied at the level of the service subnetwork exclusively. Access to the requested digital content is based on a token which is provided by the service network.